Here comes the sun

Solar panels have generated quite a bit of work as well as electricity in the last year or so. As far as I understand it, an installation needs a structural engineer’s report in order to receive accreditation. Or something.

In truth, the weight of the panels is rarely a problem. Any structure needs to be designed for a series of loads, one of which is live, or imposed, load. This is the weight of furniture and people wandering around the place. The solar panels rarely weigh more than the live load of the roof and, as the chances of someone having a party on them is slim, this is not a problem.

The problem is wind loads. The panels, especially when they are proud of the roof, act as a plane’s wing and force the roof upwards or downwards. Where the weight of the roof is less than the uplift from the wind, there is a reversal of stresses. This causes the structure to work the wrong way round and is where the fun really begins.

Most “engineered” roofs are fine. There is sufficient lattitude in the material strength to allow for the instantaneous overstress caused by wind loads. If there is a problem, the roof probably had an issue before the solar panels were applied. Most often because an owner or previous owner messed around with the roof.

So here’s a note for householders. Builders rarely leave spare bits of timber in the roof. If there one bit is attached to another bit, it is probably doing something important. If you want to remove it, you should give serious consideration to putting something else back.

Or contact your local structural engineer. They’re nice chaps. Mostly.